It is proposed to study in trained unanesthetized female dogs serving as their own controls the early and late effects of moderate and severe experimental hypertension on mean arterial pressure (MAP), cardiac output and peripheral resistance, plasma electrolytes, total exchangeble sodium (Nae), plasma renin activity (PRA), plasma renin concentration (PRC), renin substrate concentration (RSC) and plasma aldosterone concentration (PA). These same variables will be studied during the decrease of the elevated arterial pressure following release of renal artery constriction performed in the acute and chronic hypertensive state. Moderate hypertension will be produced in the uninephrectomized dog and in animals with an intact opposite kidney by graded constriction of the renal artery. Severe hypertension will be induced in the uninephrectomized animal using the same method.